Method of and apparatus for drying wood pulp and the like



March 25, 1930. R. D. KEHOE 1,751,552

METHOD OF AND APPARATUS FOR DRYING WOOD PULP AND THE,LIKE

Filed Feb. 15, 1928 3 Sheets-Sheet 1 R. D. KEHOE March 25, 1930.

METHOD OF AND APPARATUS FOR DRYING WOOD PULP AND THE LIKE Filed Fe b.15, 1928 3 Sheets-Sheet 2 Qwwzntoz RE K HOE March 25, 1930.

R. D. KEHOE METHOD OF AND APPARATUS FOR DRYING WOOD PULP AND THE LIKEFiled Feb. 15, 1928 3 Sheets-Sheet 3 Patented Mar. 25, 1930 UNITEDSTATES PATENT OFFICE RICHARD D. KEHOE, OF NEW YORK, N. Y.

METHOD OF AND APPARATUS FOR DRYING WOOD PULP AND THE LIKE Applicationfiled February 15, 1928. Serial No. 254,576.

This'invention relates to a method of and apparatus for drying woodpulp, wood chi s, bark, cellulose fibers and pulp, grains, and t e Ilike, and particularly wood pulp. I The principal object of thisinvention is to provide a commercially practical, rapid and efiicientprocess of drying materials of the character referred to above to apredetermined degree of moisture content without injury .to thematerials being treated.

Another object of this invention is to provide a process of rapidlydrying materials of the character referred to above to a predetermineddegree of moisture content wherein the extent of controlof the dryingapparatus during the drying operation is reduced to a minimum.

A further object of this invention is to provide a process for rapidlyremoving substantially all of the moisture content from materials of thecharacter above referred to without injury to such materials.

A further object of this invention is to provide a drying processcapable of rapidly 25 drying materials being treated under standardconditions of control and thereafter conditioning such materials tosecure a predetermined degree of moisture content therein.

A further object of this invention is to provide a process of dryingsubstantially wet wood pulp wherein such pulp is subjected to arelatively high temperature to remove the bulb of moisture therein,thereafter subjected to progressively decreasing temperatures, afterwhich the pulp is subjected to the action of currents of air at ordinarytemperatures, and finally suitably conditioned to provide apredetermined mosture content therein.

A further object of this invention is to provide an apparatusparticularly adapted for use in connection with the practice of my itsweight and conse uently the freight charges incident to its s ipment.The shipment of the pulp in a wet condition also possesses othermaterial disadvantages, namely, the wet pulp is greatly subject todiscoloration, and when the ulp is shipped during the winter it becomesrozen and chippers must be used for breaking the pulp into small piecesto permit its mixture with water when it is ready to be used. 'Thechippers thus employed reduce the quality of the pulp by breaking thefibres thereof. It is wholly desirable therefore to ship the pulp in adry condition, but great difliculty has been experienced in drying thepulp Without injuring the fibres thereof. As is well known, the qualityof high degree wood pulp is dependent upon the preservation of thelength of the fibres, and when the pulp is dried under the influence ofheat, the latter usually injures the fibres by charring them, and thisis particularly true if it is attempted to dry the pulp in sheet form.It has been proposed to shred the pulp before drying it, but the usualtypes of shredders have been found to cause mechanical injury to thefibres, thus reducing the value of the pulp. In the manufacture of paperstock,'the first step in the process consists in mixing or chipping thepulp in order to permit it readily to be mixed with water, and it hasbeen found that when dry pulp is provided the mixing devices may beoperated with substantially half the power ordinarily required when wetpulp is' employed, and less injury is done to the fibres. 8 The presentinvention contemplates a method wherein wood pulp, as well as othermaterials, may be rapidly dried to any desired degree of moisturecontent without appreciable injury to the material being treated therebyavoiding the disadvantages above referred to.

In the accompanying drawings I have shown a preferred form of apparatusparticularly adapted for use in the practice of my process. In thisshowing,

Figure 1 is a side elevation, parts being cut away,

Figure 2 is a plan view,

Figure 3 is a sectional view taken on line 3-3 of Figure 1, I

Figure 4 is a section taken on line 44 of Fi ure 2,

igure 5 is a detail longitudinal trans verse section, and,

' drier 11 of standard construction to which the material to be treatedis delivered through the pipe 12 from the reservoir 13 wherein thematerial in finely' divided condition is disposed in a body of liquid14. From the drum drier 11 the, material is conveyed by a belt conveyoror felt 15 to a pair of expressing rollers 16 of usual construction fromwhich the material is carried in the form of a sheet 17 througha secondpair of rollers 18 to a breaking-up device 19 which is of any suitableconstruction capable of dividing the sheet material into shredded orfinely divided form Without material injury to the fibres thereof. Thepreliminary drying apparatus 10 is well known in the art and per seforms no part of the present invention.

The breaking-up device or shredder 19 is 4 preferably arranged over abin or hopper 2O having arranged therein a conveyor 21 which is adaptedto deliver thefinely divided material in the hopper 20 to a moving belt22 which carries the material into a first stage drying chamberdesignated generally by the reference numeral 23. The chamber 23 is ofbox like construction and is divided longitudinally thereof bypartitions 24 and 25 into three compartments 23, 23, and 23. Travclingconveyors 26 and 27 carried by suitable rollers 28 are arranged incompartment 23 below the conveyor 22. Each of the conveyors travels in adirection opposite to that of the adjacent conveyor, the conveyors beingdriven by any suitable means (not shown). The compartment 23communicates with the central compartment 23 through a plurality ofopenings 29 adjacent the upper portion of the chamber 23 and a pluralityof openings 30 adjacent the lower portion of the chamber 23. A pluralityof heating coils 31 are arranged in the central compartment 23 as shownin detail in Figure 3, and a plurality of fans 32 driven in any suitablemanner as by means of a motor 33 are arranged in the openings 29 andadapted to force air from the central compartment 23 into compartment23, the heated air passing into the latter. compartment through theopenings 29 and being returned to the heating compartment through theopenings 30. An exhaust by forming a plurality 0 pipe 34 extends throughthe outer casing of the chamber 23 and communicates with the centralcompartment 23 to conduct off heated air exhausted therefrom by means ofa fan 35 arranged in the pipe 34. The conveyor 27 extends through anopening 36 in the outlet end of the first stage drying chamber 23 intothe second stage drying chamber designated generally by the referencenumeral 37.

The drying chamber 37 comprises an elongated box-like casing dividedlongitudinally thereof by means of a partition 38 extendingsubstantially vertically throughout 'a portion of the height of thechamber 37. At one side of the chamber 37, shafts 39 are arranged inopposite ends of the casing and each of,

the shafts carries a roller 40. An apron or endless conveyor 41,preferably formed of flexible wire mesh, passes aroundthe rollers 40.Any suitable means may be provided for driving the shafts 39, the speedof rotation being relatively slow for a purpose to be described. Abovethe conveyor 41 a plurality of transverse partitions 42 extend betweenthe outer walls of the chamber 37. The transverse partitions 42 aresecured to the top of the casing 37 in any suitable manner and thebottom edges of the partitions are spaced from the conveyor 41. It willbe apparent that the transverse partitions divide the upper portion ofthe chamber 37 into a plurality of compartments. A plurality of heatingcoils 45 are arranged in each of these compartments and, as shown indetail in Figure 4, extend across the entire upper portion of theheating chamber 37. One outer wall of the chamber 37 is stepped-in as at46, 47 and 48. A plurality of vertical partitions 49 extend from the topto the bottom of the elongated compartment between the central partition38 and outer stepped-in wall therecompartments 52. As clearly shown, thecompartments 52 progressively decrease in size toward the outlet end ofthe chamber 23 for a purpose hereinafter to be described.

In each of the compartments 52 are arran ed a plurality of heatinterchangers 56 preferably of the corrugated plate type and these heatinterchanges progressively decrease in size toward the outlet end of theI chamber 37. The heat interchangers seareber 74 from the charm the sump61 is inclined toward the inlet end of the casin 37 for a purposehereinafter to be describef. A lurality of pipes 62 provided with spacenozzles 63 are arranged below the conveyor 41 and extend substantiallythroughout the length of the chamber 37. Elongated deflectors 64 arearranged below the pipe 62 and extend over the shoulders of thefoundation as shown in Figure 4. The portion of the chamber 37 below theconveyor 41 is connected to each of the compartments 52 by means of aplurality of openin s 65 having staggered air deflectors or be es 66arranged therein. Below the heat interchangers 56 are arranged aplurality of fans 67 carried by the lower ends of shafts 68 suitablyjournalled in supporting frames 69. The shafts 68 extend upwardlythrough the compartments 52 and are rotated in any suitable manner asfor example, by means of motors 70 arranged on the top of the casing 37The chamber 37 adjacent the forward end thereof is provided with a hotair exhaust pipe 71 having an exhaust fan 72 arranged therein. Thechamber 37 is also provided adjacent the outlet end thereof with an airinlet pipe 73.

An atmospheric chamber designated generally by the reference numeral 74is arranged adjacent the outlet end of the chamber 37 and is providedwith an air inlet 75 and an exhaust stack 76 having an exhaust fan 77arranged therein. A closure member 78, preferably a flexible curtainseparates the chamber 37. An endless conveyor 79 is arranged in thelower portion of the chamber 74 and is adapted to receive materialdischarged from the conveyor 41. A pair of vertically arranged endlessconveyor belts 80 are arranged adjacent the delivery end of the conveyor79 and are ada ted to receive material therefrom and b rictionalengagement carry such material upwardly and deliver it to an endlessconveyor 81 extending into a conditioning chamber designated generallyby the reference numeral 82.

The conditioning chamber 82 is substantially identical in structure withthe first stage heating chamber 23 and is provided with endless conveyorbelts 83 and 84 arranged below the conveyor 81. Each of such conveyorsis designed to move in a direction opposite to that of the next adjacentconveyor belt. The chamber 83 is divided substantially centrally thereofinto two compartments by means of a partition 85. In the one of thesecompartments is disposed a plurality of heating coils 86 extendingsubstantially throughout the height of such compartment. Circulation ofair through the conveyor compartment and the heating compartment of thechamber 83 is provided by means of fans 87. The lower conveyor beltextends through an opening in the outer end of the chamber 82 whichopening. is closed by a suitable closure. member 88, preferably a.flexible curtain. The chamber 82 is provided with an air exhaust pipe 89connected to a discharge ipe 90 having a valve or damper 91 therein andto a pipe 92 having a valve or damper 93 therein which pi e is connectedto the air. inlet pipe 73 of t e chamber 37 I As heretofore stated whilemy process and apparatus may be employed in connection with variousmaterials they are particularly adapted for use in connection with thedrying of substantially wet wood pulp and it is in connection with suchmaterial that the preferred practice of my process and operation of theapparatus are hereinafter described.

The operation of the apparatus is as follows:

In the preferred practice of my process finely divided wood pulp isintroduced into a body of water in the reservoir 13 and conductedtherefrom through the pipe 12 into the drum drier 11 where in a knownmanner a substantial proportion of the water contained in the pulp isremoved. The partially dried pulp is then carried on the felt 15 to thepressure rolls 16 where an additional amount of water is removed and thepulp is formed into a sheet 17 which is carried between the ressurerolls 18 to the breaking-up device 19.

y this preliminary drying treatment approximately from 40 to 50 per centof the water in the pulp will be removed. The pulp in finely dividedcondition is dropped from the breaking-up device into the bin 20 and iscarried by the conveyor 21 to the belt 22' which in turn conveys thematerial into the first stage drying chamber 23. The delivery end of theconveyor 22 is so arranged as to deposit the finely divided pulp uponthe conveyor 26 which moves in an opposite direction therefrom. Thisconveyor then discharges the material upon the oppositely movingconveyor 27 which carries the material out of the chamber 23 to thechamber 37 and deposits it on the coveyor 41. Although wood pulp in drycondition is easily injured by the action of excessive heat, if asubstantial amount of water is present in the pulp it may be heated torelatively high temperatures since the water content fprotects the pulpfrom the charring action 0 the heat. Hence, a temperature from 250 to300 F., is preferably maintained in thevchamber 23 by means of theheating coils 31. Air withdrawn through the openings 30 into the chamber23 wherein it is heated is forced by means of the fans 32 into thechamber 23 and circulated downwardly therethrough thereby heating thepulp to the desired degree whereby a substantial proportion of theremaining water content of the pulp is removed. It will be apparent thatby arranging the conveyors in the chamber 23 as shown and described arelativelylong heating action may be secured in a relatively smallchamber. Moreover, it will be apparent that the speed of movement of theconveyors may be regulated according to the percentage of water presentin the pulp, the greater the amount of water the slower the speed ofmovement through the chamber 23.

The partially dried pulp delivered from the conveyor 27 to the conveyor41 travels along the upper apron toward the outlet end of thechamber 37The rolls 4O revolve rela tively slowly, thus causing the pulp to travelat a relatively slow linear speed through the casing 37. If desired, theshredded pulp may be periodically agitated or turned by anv suitabledevice (not shown) to present different sides of the pulp pieces to theaction of the drying medium. While it is contemplated that anyconventional turningJdeViceS necessary for the purpose may e usedthroughout the length of the conveyor 41, it is to be particularly notedthat incident to the relative disposition and arrangement of therespective conveyors 22, 26, 27 and 41 that v the pulp in more or lessshredded condition is i turned in falling from one conveyor to the nextsucceeding conveyor; that is to say, the material in being dellveredfrom one conveyor to the next in series will, in falling through thespace from the pulp receiving surface of one conveyor to the pulpreceiving surface of the next conveyor, be caused to turn or rearrangeitself with respect to its position on the preceding conveyor, so thatthrough this means the pulp is turned or rearran ed in order that a moreeffective heating 0 the pulp particles is possible than if suchparticles remained in one position throughout the transit through thedrier. During the passage of the pulp through the chamber 37 from theinlet toward the outlet end thereof, a counter current of air will becreated in the chamber by the fan 72 and discharge pipe or stack 71.'The air delivered into the chamber 37 from the pipe .73 passes beneaththe apron 41 and during its passagev through the chamber will be pickedup by the first pair of fans 67 adj acent the outlet end of the chamberand forced upwardly through the heat interchangers 56 arrangedthereabove. During the passage of air through the heat interchangers itwill be preliminarily heated and after passing through the heatinterchangers 56 will be heated to an additional extent by contact withthe coilsarranged in the top of the chamber 37. The air will then bedirected downwardly onto the shredded pulp on the apron 41. The nextpair of fans 67 tends to pull the air downwardly through the mesh of theapron thus causing it to pass against and around the pulp thereon. Thesecond pair of fans will repeat the operation of the first pair, the airpulled downwardly through .the

apron being forced into the second heating compartment wherein it isheated by the heat interchanger and the coiltherein. This action will berepeated throughout the length of the apparatus. When the air reachesthe forward end of the apparatus it will be discharged through the stack71.

As previously stated the pulp when in dry condition is easily injured bythe action of excessive heat and accordingly air delivered to thechamber 37 from the pipe 73 is supplied at a temperature notsubstantially in excess of 120 F. However, as the air reaches portionsof the pulp containing greater percentages of water it may be heated tohigher temperatures as will be apparent. Accordingly each successiveheating compartment from the outlet to the inlet end of the chamber 37is adapted to progressively increase the temperature of the dryingmedium, the temperature being increased in proportion to the increaseofthe water content of the pulp. For this reason the heat interchangers56 which are supplied with hot air from the chamber 23 by means of thepipe 34 progressively decrease in size from the inlet to the outlet endof the apparatus. The degree or increase of the temperature in eachsuccessive compartment of the chamber 37 is dependent upon thepercentage of water in the pulp delivered at the inlet end of theapparatus. In the first compartment of the chamber 37 adjacent thechamber the temperature is maintained at approximately from 200 to 250F. The next adjacent compartment is referably maintained at atemperature of rom 175 to 200 F. The next compartment is preferablymainta ned at a temperature of from 150 to 175 F. and the lastcompartment is maintained at from 120 to 150 F. It will be apparent thatif the chamber 37 is made up of a greater or less number of compartmentsthe range of temperature in each compartment will be modifiedaccordingly.

Unless provision be made in the chamber 37 to avoid it, finely dividedportions of the pulp, commonly known as dust or linters,

will be entrained in the currents of air and carried through the heatingcompartments and deposited on the heating coils whereby the finelydivided pulp Will be charred. Hence, in the final product there will bea substantial proportion of charred pulp. In order to avoid thiscondition I provide sprays of water from the pipe 62 through the nozzles63 in the portion of the chamber 37 below the conveyor 41. Any finelydivided pulp passing downwardly from the conveyor 41 in the current ofair is entrained in the spray of water and carried downwardly with thewater into the sump 61. The sump is inclined toward the forward end ofthe chamber 47 and hence the water and the pulp in the sum will bedirected toward the forward end of t e apparatus. From this point thewater and the pulp may be disposed of as desired. If a substantialamountof finely divided pulp is present in the water it may be conductedfrom the sump 61 into the reservoir 13 by any suitable means (notshown), whereby such finely divided pulp may be recovered. Theemployment of sprays of water in the chamber 37 below the conveyor 41has another and highly important advanta e. The water serves to cool theair after it as passed through the shredded pulp on the conveyor 41whereby its capacity for-further drying is materially increased as willbe apparent.

After the pul has passed through the chamber 37 it is elivered by theconveyor 41 into the atmospheric treating chamber 74 where atmosphericair, which may be dehumidified if desired, is introduced through theinlet 75 and circulated in the chamber and withdrawn by means of the fan77 and the stack 76. The temperature in the chamber 74 is maintained atapproximately from 50 to 80 F. Such treatment serves to lower thesensible heat of the pulp with the resulting removal of additionalamounts of moisture from the pulp. After the pulp has passed across thelower ortion of a c amber 74 on the conveyor 7 9 it is'carried upwardlyby means of the conveyors 80 and delivered to the conveyors 81 whichcarry the pulp into the conditioning chamber 82.

In the conditioning chamber 82 the pulp is carried downwardly by meansof the conveyors 83 and 84 in a manner similar to that in the chamber23. During the passage of the pulp through the conditioning chamber 82air is circulated through the pulp by means of the fans 87 and the airheated to the desired degree by means of the coils 86. In the preferredpractice of the process the temperature in the chamber 82 is maintainedat approximately from 100 to 150 F. Moreover, the humidity in theconditioning chamber 82 is controlled by any suitable humidifying device(not shown) so that the pulp as finally discharged from the conditioningchamber 82 will have a predetermined degree of moisture content therein.After passing through the chamber 82 the pulp is discharged by theconveyor 84 through the outlet opening and is then ready for shipment.

In the event that temperatures approching the upper limit of the rangeof temperatures preferably employed in the chamber 82 is employed in thepractice of the process the heated air discharged from the chamberthrough the pipe 89 is preferably conducted through the pipe 92 to thepi e 73 from which the air is introduced into t e outlet end of theheating chamber 37. If desired the heating the passage of pulptherethrough. In

the usual processes a difierence in external temperatures or humiditynecessitates variation of control at numerous points throughout theapparatus in order to produce a standard product. In my device howeverthe conditions throughout the apparatus, except in the conditioningchamber 82, may be kept constant regardless of external conditions oftemperature and humidity. Since such external conditions affect themoisture content of the pulponly within a relatively small range suchconditions may be compensated for in the conditioning chamber 82 inorder to provide a standard product. Hence, a defi-' nite control ofonly one part of the apparatus is required.

Another important advantage of my apparatus is that the amount of fuelnecessary to heat the drying medium is materially reduced by employingthe heated air discharged from one set of chambers for heating the airin others of the chambers. While, broadly, this is merely theapplication of the principles of heat interchange, it will be apparentthat these principles are applied in a novel manner in my apparatus.

As will be understood when the process and apparatus are employed inconnection with the drying of materials other than wood pulp theconditions of temperature will be varied according to the nature andmoisture content of material being treated.

While I have described in detail the preferred practice of my processand the preferred form of apparatus to be used it will be understoodthat the details of procedure the air is directed after passing throughthe pulp, to thereby initially raise the temperature of the air, andmeans for directing the exhaust from the rimary heating chamber throughsaid heat interchangers for heating the latter.

2. A pulp drying ap aratus, including a primary heating cham er, heatingmeans therein, a plurality of superimposed relatively reversed conveyorsin said chamber, a secondary heating chamber, a plurality of independentheating zones in such secondary chamber, a plurality of heatinterchangers in said secondary chamber, connections between said heatinterchangers and the primary heating chamber, and a single pulpconveyor moving through all zones of the secondary heating chamber.

3. A pulp drying apparatus including a primary heatin chamber, airheating means therein, a plura ity of superimposed relatively reversedpulp conveyors in said chamber, .a secondar heating chamber including aseries of in ependent heating zones, air heating means in each zone,means for utilizing the exhaust from the primary chamber for partlyheating the air of each zone after passage of the air through the pulp,a single conveyor operative through all zones of the secondary chamber,means for forcing heated air through the pulp on the conveyor, and meansoperative below the conveyor for clearing the air of suspended pulpparticles.

' 4. A pulp drylng apparatus including a primary heating chamber, airheating means therein, a pul conveyor therein, a secondary heating chamer, a single pulp conveyor operative therein, a plurality ofsuccessively decreased heating units in said secondary heating chamber,means for forcing heated air through the pulp on the conveyor at aplurality of spaced points in the travel of the pulp, and means forspraying the air below the conveyor with water.

5. A pulp drying apparatus including a primary heating chamber, aplurality of superimposed relatively reversed conveyors in said chamber,air heating means in said chamber, means for forcing the heated airthrough the pulp on said conveyors, a secondary heating chamber, asingle conveyor operative therein, a plurality of heating means in saidsecondary chamber, each of said heating means being of progressivelyless heating effect in the direction of travel of the material, meansfor forcin air heated by the said heating means throug the pulp on theconveyor, an atmospheric chamber, a conveyor therein to receive the pulpfrom said single conveyor, and a conditioning chamber to regeive thepulp from the atmospheric cham- 6. A pulp drying apparatus including aheating-chamber, a pulp conveyor moving longitudinally of the chamber,means in the chamber for heating said air through the ulp on theconveyor, and a spray arranged elow the conveyor for clearingthe air ofsuspended pulp particles after the air has passed through the pulp.

7. A pulp drying apparatus including a base, a heating chambersupported'thereon, a pulp conveyor movable longitudinally of thechamber, heating means arranged in the secondary heating chamber havinga plurality of heating zones therein, a single material -conveyor forcarrying the material through all of said zones in succession, means fordirecting a current of air longitudinally of the secondary heatingchamber in a direction opposite that of the travel of the material, airheating means in each zone including a preliminary'heating element and afinal heating element, means for directing the exhaust of the primaryheating chamber through the preliminary heating elements of all zones ofthe secondary heating chamber, and means for delivering air from saidair current from beneath the material on the conveyor to a positionabove said'material, said means causing the air to be heated insuccession by the preliminary heater and final heater.

9. A pulp drying apparatus including a primary heating chamber, airheating means therein, a pulp conveyor therein, a secondary heatingchamber, a single pulp conveyor operative in said secondary heatingchamber, and a plurality of air heating means arranged in distinctiveheating zones in said secondary heating chamber, each of said airheating means including a heat interchanger heated by the exhaust fromthe primary chamber and an independent heating coil.

10. A pulp drying apparatus including a primary heating chamber, airheating means therein, a pulp conveyor therein, a secondary heatingchamber, a single pulp conveyor operative in said secondary heatingchamber, and a plurality of air heating means arranged in distinctiveheating zones in said secondary heating chamber, each of said airheating means including a heat interchanger heated by the exhaustfromthe primary chamber and an independent heating coil, the heatinterchangers and heating coils of each heating means being ofdecreasing heating effeet in the direction of travel of the material.

11. A pulp drying apparatus including a plurality of heating chambers,each provided with means for supplying heat at varying temperatures, aplurality of superimposed independent conveyors for carrying the pulpair, means for directing through said plurality of heating chambers,said conveyors being arranged to receive the pulp in succession one fromthe other, the pulp particles in delivery from one conveyor to the nextsucceeding conveyor being permitted a free falling movement, whereby theparticles have a tendency to change their relative positions andrelations on each succeeding conveyor, to permit a more effectiveheating of the respective particles, the final con- 1 veyor passingsuccessively through heating chambers which are of gradually reducedtemperatures toward the outlet end of the apparatus, means forsubjecting the dried pulp to atmospheric treatment after passing throughthe last one of the heating chambers, and means at the outlet end of theapparatus for conditioning the particles of pulp passed through theheating chambers after the pulp has been subjected to atmospherictreatment.

In testimony whereof I aflix my signature.

RICHARD D. KEHOE.

